The Selectivity-Sensitivity Compromise

The term sensitivity is widely used in two rather different ways. Firstly, it is widely used colloquially in a somewhat loose undefined maimer to refer to (but not evaluate) the magnitude of the analytical signal produced by introduction of some (usually unspecified) amount of analyte into the mass spectrometer. Alternatively, this colloquial usage sometimes implies a reference to the smallest quantity of analyte that can be detected or quantitated (i.e., the LOD and LLOQ, Section 8.4). However, in a more rigorous usage, the sensitivity of either an 

It is now possible to move on to discussion of general parameters of a mass spectrometer that are relevant to the selectivity-sensitivity compromise that is ubiquitous in analytical chemistry. Full scan acquisition mode refers to operation of a mass analyzer so as to acquire the entire spectrum of ions (or a major portion thereof) introduced into the analyzer. In the case of a pure compound, full scan mode delivers the maximum chemical information that the mass spectrometric experiment (MS or MS/MS) can 

Finally in this section, it can be mentioned that there is a tendency in the literature to use the terminology full scan mode to refer only to acquisition of a complete mass spectrum, i.e., ignoring the fact that it is also perfectly feasible to obtain a complete spectrum in MS/MS mode 

This section deals with some general principles of tandem mass spectrometry and its applicability to quantitative analysis. The MS/MS acronym is used in this book as a general term for aU tandem mass spectrometry techniques. More detailed descriptions of how the principles are exploited in practice for the various instrumental types are given in later sections of this chapter. The general concept of tandem mass spectrometry in qualitative (structural) analysis is that additional chemical information, over and above that contained in a conventional onedimensional mass spectrum, can be obtained by examining the connectivity relationships among some or all of the ions in that mass spectrum. The connectivities arise as a result of the dissociation reactions that lead to the fragment ions in a mass spectrum, e.g.  

In a somewhat different theoretical approach based on information theory, and using an example directly pertinent to the concerns of this book (Fetterolf 1984), the logic gates concept is replaced by that of informing elements such as clean-up procedure, chromatographic retention time, ionization efficiency with a particular technique, selection of mJz values of a precursor ion and of one or more product ions (possibly via more than one stage of 

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